One problem encountered with conventional tool holders is that of holding the cutting insert securely in the pocket of the tool holder. At the beginning of a cutting operation, the sudden transition from no load to extreme pressure load on the insert can cause the insert to shift position in the holder and thereby affect the accuracy of the planned cut. At the end of the cutting operation, the sudden disengagement of the cutting insert from the workpiece causes the pressure load suddenly to be removed from the insert. This sudden change in load can cause the insert to shift and distress any repeatable dimensional accuracy, which is essential for most tool holders, especially cutting inserts used in Numerically Controlled machines, to meet.
During the cutting operation, loads of up to 35,000 pounds may be encountered on the cutting insert which, if the insert is not precisely located and firmly held in the holder to begin with, can also cause shifting of the insert during the cutting operation. It is, therefore, important to provide a tool holder that can precisely and securely seat a cutting insert and then securely hold the cutting insert in location during all phases of the heavy duty cutting operation.
When taking a heavy duty cut, such as described above, the efficiency of removing the metal from a workpiece is, thus, to be maximized. The rate of metal removal rate from a workpiece is, however, only one part of the efficiency factor. When using indexable cutting inserts, there comes a point in time when the cutting edge becomes worn and must be replaced with a fresh cutting edge.
To change a cutting edge, the cutting action must be stopped and the machine operator must index the cutting insert to a new cutting edge or replace the cutting insert altogether if all of the cutting edges thereof have become worn. The time it takes the operator to make this change directly affects the efficiency or metal removal rate of a particular machine.
The operator, having stopped the machine after some very heavy duty cutting, now has the situation that the insert the operator is about to change or index is extremely hot; in fact, too hot to be handled without gloves, rags, or other protection by the operator. Most gloves and other protection worn by the operator are cumbersome to them and, therefore, any system used for locating and seating a cutting insert in a tool holder, should recognize that a minimum of tools should be used at this point, or that if tools are used, they should be of sufficient size and utility to be used by the operator while using gloves or other protective equipment.
Most of the pin type holders of the prior art may be defective in that the pin-type clamp merely holds the insert down in the pocket without insuring that the insert is positioned or held back against one side wall of the pocket, or the pin-type holders mainly hold the insert back against a side wall of the pocket without holding the insert down in the pocket and, therefore, did not prevent fluttering of the insert during extreme operating conditions.